1. Field Of The Invention
The present invention relates generally to a spirometer. Specifically, this invention relates to a spirometer which measures the breathing volume or breathing rate of human subjects by sensing the back pressure developed in an open chamber through which the subject breathes. The chamber has an opening which varies in size so that the spirometer may provide accurate pressure readings over a wide range of flow rates.
2. Description Of The Prior Art
Spirometers measure the breathing volume or breathing rate of human subjects. For many applications, these devices require a simple construction to minimize malfunctions. They should also have a portable construction to allow a user to test human subjects at any one of a wide variety of locations, e.g. various industrial environments or at the bedside of a hospitalized patient. Moreover, they should provide precise, uniform and reliable performance.
Many prior art spirometers include a closed but distensible chamber into which a subject exhales or from which the subject inhales. The chamber expands or contracts in response to the force provided by the breath; and the spirometer measures the change in volume of the chamber. These prior spirometers are bulky and have a multiplicity of close tolerance components which make them susceptible to malfunctions and breakdowns. They also do not include any means for avoiding rebreathing cross-contamination Finally, producing these prior art spirometers requires accurate and expensive machines and machining techniques, complicated and time-consuming assembly processes, and the use of costly materials.
Other prior spirometers have open chambers; and they measure the back pressure of the breath which moves through the open chamber. Screens, grids, or filter papers placed over the opening through which breath moves in and out of this chamber constrict the flow of breath. Typically, this opening has a fixed diameter which does not allow the apparatus to measure pressures over a wide range of flow rates.
Still other prior spirometers have housings which define a chamber with an opening and which include a flexible material for defining the opening and allowing a user to vary its size. However, the structures and materials which provide these openings introduce a wide variety of complexities and disadvantages in these prior spirometers. These complexities make them susceptible to malfunctions and breakdowns and render them unreliable.
The spirometer of the present invention provides a construction which minimizes the expense of manufacture and assembly and gives precise, uniform and reliable performance. It comprises a small number of components which allow the user to measure breathing volume or flow rates of human subjects by taking pressure measurements over an extended range of breath flow rates. This spirometer includes a mouthpiece/transducer which is inexpensive and disposable and which does not require calibration.